Approximately 33% of the American population suffers from obesity. Complications for those significantly overweight include heart disease, diabetes, and stroke. Adipocytes in fat tissue display substantial hypertrophy in obese individuals. Each adipocyte is surrounded by a basal lamina, a specialized extracellular matrix (ECM) composed primarily of collagen IV and laminin, whereas the stromal ECM of fat, the interstitium that tethers and supports the vasculature and adipocytes within the tissue, is composed in large part of fibrillar collagen I. During obesity, as adipocytes hypertrophy, the ECMs of the basal lamina and stroma expand to accommodate the growing cells and tissue. As ECM provides structural support and regulatory cues to cells in tissues, ECM in fat undoubtedly acts to influence adipocyte biology in obesity. However, relatively little is known about the nature of ECM in adipose and changes that might occur in its structure and composition in response to fat cell hypertrophy. We hypothesize that specific components of the FCM of adipose tissue affect adipocyte cell behavior, and specifically, in hypertrophy. In Aim 1, we propose to characterize the composition of the ECM in fat from mice of normal weight, determine the contribution made by the 3 major compartments of the fat (adipocyte, stroma, and vasculature) to the ECM, and determine changes in the ECM that occur during growth associated with development. We will also investigate the regulation of collagen I, the primary component of the stromal ECM, in primary fibroblasts isolated from adipose tissues. Results from Aim 1 will then be used in Aim 2 as a base line of ECM structure and composition to compare to two models of adipocyte hypertrophy-- nutritional obesity and SPARC-null mice. SPARC-null mice display substantial increases in adiposity without significant differences in overall body weight. As previous studies of SPARC-null mice have revealed aberrations in the collagenous ECM of dermis and in the basal lamina of lens capsule, we predict that the observed increase in fat accumulation in these mice might be based, at least in part, in compromised functional properties of adipose ECM. Alterations in the adipose ECM of SPARC-null mice will be compared to ECMs of nutritionally obese mice to discern expression of specific ECM components associated with adipocyte hypertrophy. In addition, two growth factors shown to influence ECM deposition TGF-betal and leptin, will be assessed for their capacity to affect adipocyte and stromal fibroblast ECM synthesis and deposition. These experiments will provide valuable information on the formation of ECM in adipocyte hypertrophy that will be critical for a complete understanding of the life cycle of the adipocyte.